Roadway inspection holes generally consist of a frame fastened to the roadway and of a removable pad. In order to gain access to the subsurface structure through the inspection hole, the cover must be removed. This operation is inconvenient whatever the weight of the pad may be. The same applies when the pad is to be put back into the frame.
Furthermore, in order to prevent the pad from being uplifted when a heavy vehicle passes above it, thereby giving rise to a strong vertical suction, and also in order to prevent any accident as the inspection hole is opened, heavy and massive pads, held in place only by their weight, are being progressively replaced by articulated pads of the type described in British Pat. No. 474,250 and in French patent application No. 79.06566. Experience has shown that it is desirable, on the one hand, to facilitate the opening and closure operations of the pads by controlling the pivoting movements and, on the other hand, to prevent the articulating means from being clogged up by earth or other waste material which might come into the fissures of the inspection hole and thus might interfere with their operation.
Manholes are known, in particular from U.S. Pat. No. 2,997,932, which comprise two half-pads each shaped as a right angled isosceles triangle, which are placed side by side on the frame through their hypotenuse and are provided, within the latter's extension and that of their angle, with radial lugs of trapezoidal section resting on bearings with a V-shaped complementary section. In this arrangement, each half-pad rests on the frame at only three points which gives it excellent stability and prevents it from producing noises when heavy vehicles are passing over.